In the field of electronics, in response to demands for higher speeds and larger capacity, smaller size and lighter weight of electronic equipment, the development of mounting technology for realizing a higher degree of integration and higher density of electronic parts such as semiconductor chips and discrete parts is being advanced. One mounting technique for such semiconductor devices which has been proposed is the flip chip mounting method using bare chips.
In the flip chip mounting method, first, a plurality of electrode pads are formed on a bare chip, and bumps made of solder, gold, or the like are formed on the electrode pads. Then, in order to join the bumps of the bare chip and the circuit electrodes of a substrate (referred to below as lands), the surface of the bare chip on which the electrode pads are formed is made to oppose the surface of the substrate on which the lands are formed, and the electrode pads are electrically connected to the corresponding lands. In order to guarantee an electrical connecting strength and mechanical bonding strength between the bare chip and the substrate, after the pads and the lands are joined to each other in the above-described manner, the underfill method, in which a resin is made to flow and the bare chip and the substrate are secured to each other, is sometimes also carried out.
When performing mounting of an electronic part such as an optical device having a low heat resistance temperature, in order to prevent thermal degradation of the electronic part, it is necessary to join the electrode pads (bumps) and the lands at a low temperature. The flip chip mounting method using an electrically conductive adhesive such as an anisotropic conductive film (ACF) or an anisotropic conductive paste (ACP) has been proposed as a technique which can perform such low temperature bonding (see, for example, Patent Documents 1, 2, and the like).
The above-mentioned electrically conductive adhesive is a material for connecting electrodes which can provide electrical conductivity between electrode pads (bumps) and lands (referred to below as opposing electrodes) and provide insulating properties between adjoining electrode pads and adjoining lands (both referred to below as adjoining electrodes) by dispersing electrically conductive particles of a metal or the like in a resin. Namely, electrical conductivity between opposing electrodes is made possible by the electrically conductive particles contained in the electrically conductive adhesive, while insulation between adjoining electrodes is guaranteed, opposing electrodes are adhered to each other, and the bare chip and substrate are secured to each other by the resin contained in the electrically conductive adhesive.
In the above-described electrically conductive adhesive, normally, electrically conductive particles are uniformly dispersed in a resin. The dispersed electrically conductive particles physically contact the electrode pads (bumps) and the lands, as a result of which electrical connection between opposing electrodes is made possible.
However, when using an electrically conductive adhesive having electrically conductive particles uniformly dispersed in a resin in the manner described above, there is the possibility that the electrically conductive particles contained in the electrically conductive adhesive cannot be effectively utilized for providing electrical conductivity between opposing electrodes. Namely, the electrically conductive particles are uniformly dispersed in the resin, and it is thought that the electrically conductive particles which contribute to conductivity between opposing electrodes are a portion of the electrically conductive particles contained in the electrically conductive adhesive (see Non-patent Document 1). Therefore, with an electrically conductive adhesive, there is the possibility that adequate reliability of electrical connections between opposing electrodes cannot be obtained, and in addition, the electrically conductive particles which do not contribute to conductivity between opposing electrodes obstruct electrical insulation between adjoining electrodes. Furthermore, the electrically conductive particles contained in the electrically conductive adhesive cannot be effectively utilized, and it is difficult to realize decreases in cost.
In Patent Document 3, particles which have an aligning effect by electric field, and they are aligned in the direction of an electric field upon the application of an electric field are used as electrically conductive particles. Namely, in Patent Document 3, an electrically conductive bonding agent is supplied between a bare chip and a substrate, and opposing electrodes are electrically connected to each other by applying an electric field to this electrically conductive adhesive and aligning the electrically conductive particles.
Patent Document 1: International Patent Application Publication Number WO 2000/57469 (published on Sep. 28, 2000)
Patent Document 2: Japanese Published Unexamined Patent Application Hei 10-4126 (published on Jan. 6, 1998) (Heisei 10))
Patent Document 3: Japanese Published Unexamined Patent Application Hei 8-315883 (published on Nov. 29, 1996 (Heisei 8))
Non-patent Document 1: “Recent News Concerning Electronic Mounting Technology”, Polyfile, Volume 35, No. 3, pages 14-18, (1998)
Non-patent Document 2: Y. Ohta et al., “Research on Evaluating Properties of Joints in Resin Connections”, collected papers from the Eighth Symposium on Microjoining and Assembly Technology in Electronics, pages 169-174 (2002)